1. Field of the Invention
The present invention relates to a battery box for accommodating therein a plurality of batteries for driving an electric vehicle.
2. Description of the Related Art
As a power supply for driving an electric vehicle there has normally been used a power supply of the type wherein a plurality of batteries are electrically series-connected to one bother. When a battery of 12 V is used, for example, it is necessary to electrically series-connect nine or more batteries to one another to produce desired electric power and to mount the connected batteries to the electric vehicle. Therefore, a space for accommodating the batteries therein greatly increases.
Each of the batteries is heavy in weight. Therefore, a proposal for disposing such heavy batteries under the floor so as to lower the center of gravity of the electric vehicle has been made (see Japanese Patent Application Publication No. 51-27047, GB 1555773 A, etc.).
When, however, all the batteries are placed under the floor, crossmembers cannot be mounted between the sideframes of the vehicle body insufficiently close spacing because of the amount the space required for positioning the large number of batteries between the sideframes. It is therefore difficult to effectively maintain the rigidity of the frame of the vehicle body.
When, on the other hand, the batteries are suspended under the floor to avoid interference with the crossmembers in a state in which the batteries have been accommodated in a battery box, nine or more batteries are so heavy in weight that it becomes necessary to greatly increase the strength of the battery box for holding the batteries therein. It is therefore considered necessary to increase the thickness of the materials forming the battery box to ensure its strength. However, this creates the problem that the battery box becomes heavy in weight, thereby increasing the entire weight of the vehicle body and reducing the rigidity of the vehicle body.
It is also considered necessary to affix the battery box to a frame member by tightening members such as bolts, etc. from below the frame member in order to use the battery box as a portion of the rigid body of the vehicle. However, all the bolts, which are the tightening members, are positioned and tightened so as to extend in the vertical direction. Therefore, when an impact or the like is applied to the vehicle body so as to exert a horizontal external force on the battery box, the external force is directly exerted on the bolts as a shearing force which may result in shearing of the bolts and detachment of the battery box from the vehicle.